Agricultural and urban contaminants are an environmental concern because runoff may contaminate aquatic ecosystems, resulting in stress for exposed fish. The objective of the present controlled, field‐based study was to assess the impacts of high‐intensity agriculture and urban land use on multiple life stages of the fathead minnow (Pimephales promelas), using the Maumee River (Toledo, OH, USA) as a case study. Laboratory cultured adult and larval fathead minnows were exposed for 21 d, and embryos were exposed until hatching to site‐specific water along the lower reach of the Maumee River. Adult minnows were analyzed for reproduction and alterations to hematologic characteristics (vitellogenin, glucose, estradiol, 11‐ketotestosterone). Water and fish tissue samples were analyzed for a suite of multiresidue pesticides, hormones, and pharmaceuticals. Contaminants were detected in every water and tissue sample, with 6 pesticides and 8 pharmaceuticals detected in at least 82% of water samples and at least half of tissue samples. Effects differed by exposed life stage and year of exposure. Fecundity was the most sensitive endpoint measured and was altered by water from multiple sites in both years. Physiological parameters associated with fecundity, such as plasma vitellogenin and steroid hormone concentrations, were seldom impacted. Larval fathead minnows appeared to be unaffected. Embryonic morphological development was delayed in embryos exposed to site waters collected in 2016 but not in 2017. A distinction between agricultural and urban influences in the Maumee River was not realized due to the great overlap in contaminant presence and biological effects. Differences in precipitation patterns between study years likely contributed to the observed biological differences and highlight the need for environmental exposure studies to assess the environmental risk of contaminants. Environ Toxicol Chem 2019;00:1‐17. © 2019 SETAC

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Contaminants of emerging concern (CECs) are ubiquitous in aquatic environments with well-established endocrine-disrupting effects. A data matrix of 559 water samples was queried to identify two commonly occurring CECs mixtures in Great Lakes tributaries. One mixture consisted of eight agricultural CECs (AG), while another contained 11 urban CECs (UB). The known estrogenic compounds bisphenol A, estrone and nonylphenol were present in both mixtures. According to the EPA Tox21 in ToxCast database, AG and UB mixture at an environmentally relevant concentration were estimated to account for 6.5% and 3.4% estrogenicity of the model endocrine disruptor estradiol-17β, respectively. Two isoforms of the estrogen receptor (Esr1 and -2, former Erα and Erβ) cloned from fathead minnow, bluegill sunfish, American alligator and human, responded differently to AG and UB mixtures. Human and bluegill Esr1 were the most sensitive to AG and UB mixtures, respectively. Fathead minnow Esr1 and Esr2b were the least sensitive to 10× AG and UB in estrogen dose equivalents, respectively. Even at environmentally documented concentrations, UB significantly activated bluegill Esr1. Moreover, 100× concentrated UB hyperstimulated fathead minnow Esr1 beyond the maximum induction of estradiol-17β. These results indicate that efficacious receptors and species differ in their response to CEC mixtures. Furthermore, estrogenicity may be present in some CECs not previously considered estrogenic, or, alternatively, estrogenicity of a mixture may be enhanced through chemical interactions. Our study highlights the need for further studies of CECs utilizing a variety of receptors cloned from diverse species.